Human Distal Femur Research Articles

Method for accurate removal of trabecular bone samples from a curved articulating surface of the distal femur

BackgroundKnowing the mechanical properties of trabecular bone is critical for many branches of orthopaedic research. Trabecular bone is anisotropic and the principal trabecular direction is usually aligned with the load it transmits. It is therefore critical that the mechanical properties are measured as close as possible to this direction, which is often perpendicular to a curved articulating surface. Methods: This study presents a method to extract trabecular bone cores perpendicular to a curved articulating surface of the distal femur. Cutting guides were generated from computed tomography scans of 12 human distal femora and a series of cutting tools were used to release cylindrical bone cores from the femora. The bone cores were then measured to identify the angle between the bone core axis and the principal trabecular axis. FindingsThe method yielded an 83% success rate in core extraction over 10 core locations per distal femur specimen. In the condyles, 97% of extracted cores were aligned with the principal trabecular direction. InterpretationThis method is a reliable way of extracting trabecular bone specimens perpendicular to a curved articular surface and could be useful across the field of orthopaedic research.

Additional Plate Fixation of Hinge Fractures After Varisation Distal Femoral Osteotomies Provides Favorable Torsional Stability: A Biomechanical Study

Background: Hinge fractures are considered risk factors for delayed or nonunion of the osteotomy gap in distal femoral osteotomies (DFOs). Limited evidence exists regarding the treatment of hinge fractures after DFO, which could improve stability and thus bone healing. Purpose: To (1) examine the effect of hinge fractures on the biomechanical properties of the bone-implant construct, (2) evaluate the biomechanical advantages of an additional fixation of a hinge fracture, and (3) test the biomechanical properties of different types of varisation DFOs. Study Design: Controlled laboratory study. Methods: A total of 32 fresh-frozen human distal femora equally underwent medial closing wedge DFO or lateral opening wedge DFO using a unilateral locking compression plate. The following conditions were serially tested: (1) preserved hinge; (2) hinge fracture along the osteotomy plane; (3) screw fixation of the hinge fracture; and (4) locking T-plate fixation of the hinge fracture. Using a servo-hydraulic materials testing machine, we subjected each construct to 15 cycles of axial compression (400 N; 20 N/s) and internal and external rotational loads (10 N·m; 0.5 N·m/s) to evaluate the stiffness. The axial and torsional hinge displacement was recorded using a 3-dimensional optical measuring system. Repeated-measures 1-way analysis of variance and post hoc Bonferroni correction were used for multiple comparisons. Statistical significance was set at P < .05. Results: Independent from the type of osteotomy, a fractured hinge significantly (P < .001) increased rotational displacement and reduced stiffness of the bone-implant construct, resulting in ≥1.92 mm increased displacement and ≥70% reduced stiffness in each rotational direction, while the axial stiffness remained unchanged. For both procedures, neither a screw nor a plate could restore intact rotational stiffness (P < .01), while only the plate was able to restore intact rotational displacement. However, the plate always performed better compared with the screw, with significantly higher and lower values for stiffness (+38% to +53%; P < .05) and displacement (–55% to −72%; P < .01), respectively, in ≥1 rotational direction. At the same time, the type of osteotomy did not significantly affect axial and torsional stability. Conclusion: Hinge fractures after medial closing wedge DFO and lateral opening wedge DFO caused decreased bone-implant construct rotational stiffness and increased fracture-site displacement. In contrast, the axial stiffness remained unchanged in the cadaveric model. Clinical Relevance: When considering an osteosynthesis of a hinge fracture in a DFO, an additional plate fixation was the construct with the highest stiffness and least displacement, which could restore intact hinge rotational displacement.

Sub-optimal femoral fit in total knee arthroplasty, a systematic review of human femoral data vs off-the-shelf contemporary femoral components

PurposeThe purpose of the current study is to investigate the inadequacy of fit between the human distal femur and the knee implants offerings and describe the available strategies to overcome this issue.MethodsA systematic research of the literature was performed to identify studies reporting morphologic measures of the distal femur. Studies were excluded if they included unhealthy knees or the morphological analysis did not report the two key dimensions to identify the patient’s unique anatomy: AP length and mediolateral (ML) width. Clinically relevant component overhang or underhang was considered when the metal-bone mismatch was > 3 mm as described in the literature.ResultsSix studies with anthropometric analysis of 1395 distal femurs met the inclusion criteria. The analysis revealed that by employing the available sizes of four current “state-of-the-art” primary off-the shelf (OTS) femoral implants up to 13–41% would show underhang and 9–27% overhang clinically relevant and the introduction of narrower sizes did not reduce this percentage of underhang but improved the overhang rate of 10–15%.ConclusionsWhenever an ML/AP mismatch in encountered in the operating room, adaptations are needed, and these bring about deleterious biomechanical and clinical complications. Therefore, this study highlights the need for implants design with multiple ML offerings per AP size, since they provide not only more sizes options but more femoral shapes to match the different ML sizes of the distal femur, compared to designs with single ML offerings for a given femoral AP dimension.

Post-operative fracture risk assessment following tumor curettage in the distal femur: a hybrid in vitro and in silico biomechanical approach

The distal femur is the predominant site for benign bone tumours and a common site for fracture following tumour removal or cementation. However, the lack of conclusive assessment criterion for post-operative fracture risk and appropriate devices for cement augmentation are serious concerns. Hence, a validated biomechanical tool was developed to assess bone strength, depending on the size and location of artificially created tumorous defects in the distal femora. The mechanics of the bone–cement interface was investigated to determine the main causes of reconstruction failure. Based on quantitative-CT images, non-linear and heterogeneous finite element (FE) models of human cadaveric distal femora with simulated tumourous defects were created and validated using in vitro mechanical tests from 14 cadaveric samples. Statistical analyses demonstrated a strong linear relationship (R2 = 0.95, slope = 1.12) with no significant difference between bone strengths predicted by in silico analyses and in vitro tests (P = 0.174). FE analyses showed little reduction in bone strength until the defect was 35% or more of epiphyseal volume, and reduction in bone strength was less pronounced for laterally located defects than medial side defects. Moreover, the proximal end of the cortical window and the most interior wall of the bone–cement interface were the most vulnerable sites for reconstruction failure.

Investigation on distal femoral strength and reconstruction failure following curettage and cementation: In-vitro tests with finite element analyses

Cement augmentation following benign bone tumor surgery, i.e. curettage and cementation, is recommended in patients at high risk of fracture. Nonetheless, identifying appropriate cases and devices for augmentation remains debatable. Our goal was to develop a validated biomechanical tool to: predict the post-surgery strength of a femoral bone, assess the precision and accuracy of the predicted strength, and discover the mechanisms of reconstruction failure, with the aim of finding a safe biomechanical fixation. Tumor surgery was mimicked in quantitative-CT (QCT) scanned cadaveric human distal femora, and subsequently tested in compression to measure bone strength (FExp). Finite element (FE) models considering bone material non-homogeneity and non-linearity were constructed to predict bone strength (FFE). Analyses of contact, damage, and crack initiation at the bone-cement interface (BCI) were completed to investigate critical failure locations. Results of paired t-tests did not show a significant difference between FExp and FFE (P > 0.05); linear regression analysis resulted in good correlation between FExp and FFE (R2 = 0.94). Evaluation of the models precision using linear regression analysis yielded R2 = 0.89, with the slope = 1.08 and intercept = −324.16 N. FE analyses showed the initiation of damage and crack and a larger cement debonding area at the proximal end and most interior part of BCI, respectively. Therefore, we speculated that devices that reinforce critical failure locations offer the most biomechanical advantage. The QCT-based FE method proved to be a reliable tool to predict distal femoral strength, identify some causes of reconstruction failure, and assist in a safer selection of fixation devices to reduce post-operative fracture risk.

Quantification of human bone microarchitecture damage in press-fit femoral knee implantation using HR-pQCT and digital volume correlation

Primary press-fit fixation of femoral knee prostheses is obtained thanks to the inside dimensions of the implant being undersized with respect to the bone cuts created intra-operatively, dictated by a press-fit specified by the implant design. However, during prostheses press-fit implantation, high compressive and shear stresses at the implant-bone interface are generated, which causes permanent bone damage. The extent of this damage is unknown, but it may influence the implant stability and be a contributing factor to aseptic loosening, a main cause of revisions for knee arthroplasty. The aim of this ex-vivo study was to quantify, using high-resolution peripheral quantitative computed tomography (HR-pQCT) imaging and Digital Volume Correlation (DVC), permanent bone deformation due to press-fit femoral knee implantation of a commonly used implant. Six human cadaveric distal femora were resected and imaged with HR-pQCT (60.7 μm/voxel, isotropic). Femurs were fitted with cementless femoral knee implants (Sigma PFC) and rescanned after implant removal. For each femur, permanent deformation was examined in the anterior, posterior-medial and posterior-lateral condyles for volumes of interest (VOIs) of 10 mm depth. The bone volume fraction (BV/TV) for the VOIs in pre- and post-implantation images was calculated, at increasing depth from the bone surface. DVC was applied on the VOIs pre- and post-implantation, to assess trabecular bone displacements and plastically accumulated strains. The “BV/TVpost/BV/TVpre ratio vs. depth” showed, consistently among the six femurs, three consecutive points of interest at increasing bone depth, indicating: bone removal (ratio<100%), compaction (ratio>100%) and no changes (ratio = 100%). Accordingly, the trabecular bone displacement computed by DVC suggested bone compaction up to 2.6 ± 0.8 mm in depth, with peak third principal strains of −162,100 ± 55,000 με (mean absolute error: 1,000–2,000 με, SD: 200–500 με), well above the yield strain of bone (7,000–10,000 με). Combining 3D-imaging, at spatial resolutions obtainable with clinical HR-pQCT, and DVC, determines the extent of plastic deformation and accumulated compressive strains occurring within the bone due to femoral press-fit implantation. The methods and data presented can be used to compare different implants, implant surface coatings and press-fit values. These can also be used to advance and validate computational models by providing information about the bone-implant interface obtained experimentally. Future studies using these methods can assist in determining the influence of bone damage on implant stability and the subsequent osseointegration.

Virtual Geometric Reconstruction of Australopithecine Femora: A Methodological Evaluation

The fragmentary nature of fossils, and the need to extract as much information from them as possible, mandates that broken portions be reconstructed. Virtual reconstruction using geometric morphometric techniques based on the thin plate spline (TPS) function can be used to locate landmarks that represent missing portions of fossil specimens. Here we evaluate the accuracy of TPS‐based reconstruction in artificially damaged australopithecine distal femora.Surface models of modern human (n=35) and chimpanzee (n=37) distal femora, as well as those of two australopiths (casts of A.L. 129‐1a and A.L. 333‐4), were created using a structured light scanner. Articular surfaces were trimmed from the rest of the surface model. 1007 sliding semilandmarks were distributed across the articular surface, and semilandmarks were then slid to minimize the bending energy of the TPS function relative to an updated Procrustes average. Fossils were then virtually destroyed by removing semilandmarks to mimic the type of destruction observed in other fossil specimens. Removed portions increased from a small, central hole in the middle of each condyle to removal of the entire condyle. Average chimpanzee and human femora were used as references to create two separate reconstructions using geometric reconstruction based on the TPS function. Procrustes distances (PD) between each reconstruction and the original fossil were calculated to evaluate reconstruction accuracy.Reconstructions based on both human and chimpanzee averages deviated further from the original fossils as the level of artificial damage increased. When the entire medial condyle was reconstructed, the original morphology of both australopithecine fossils was intermediate between the human‐based and chimpanzee‐based reconstructions. For these reconstructions, Procrustes distances indicate that both A.L. 129‐1a and A.L. 333‐4 are most similar to the human‐based reconstruction (A.L. 129‐1a: PD = 0.001 vs. 0.002; A.L. 333‐4: PD = 0.002 vs. 0.003). When the entire lateral condyle was reconstructed, the fossils fell outside the possible morphologies bounded by the human‐based and chimpanzee‐based reconstructions. Procrustes distances indicate that both fossils are more similar to the human‐based reconstructions than those based on the average chimpanzee (A.L. 129‐1a: PD = 0.004 vs. 0.005; A.L. 333‐4: PD = 0.005 vs. 0.009). These results suggest that while the australopithecine medial femoral condyle may be considered an interpolation between chimpanzee and human morphology, the lateral condyle does not follow the same trend. For australopithecine distal femur reconstructions to be accurate, medial and lateral condyles should be considered separately.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Human cartilage-bone-synovium microphysiological system to study ptoa pathogenesis and treatment on earth and in space

Purpose: Acute joint injuries from sports, exercise or accident-related trauma often progress to post-traumatic Osteoarthritis (PTOA), comprising ∼12% of all OA cases. Such joint injuries can cause mechanical damage to cartilage combined with an inflammatory response associated with the synovial lining of the joint capsule. Together, these events lead to cartilage and subchondral bone pathologies including cell death, tissue degradation, neoangiogenesis, osteophyte and cyst formation and synovial fibrosis. Astronauts on International Space Station-National Laboratory (ISS-NL) sustain a higher rate of exercise-related injuries, including those compromising joints, during their training and mission period. Acknowledging the urgent need to identify disease-modifying therapeutics to ameliorate degenerative evolution of OA/PTOA, we carried out this study to (1) simulate aspects of acute joint injury biology on earth and in space using a human Cartilage-Bone-Synovium coculture model (CBS-MPS), (2) to investigate the potential of dexamethasone (Dex) in reducing cell death and ECM degradation, and (3) to utilize a Multi-Use Variable-g Platform (MVP) to study PTOA-related pathogenesis and management on the ISS. Methods: Osteochondral plugs (3.5mm diameter and 5mm thick, including 1.5-2mm thick cartilage) harvested from condyles and trochlear grooves of cadaveric human distal femurs (n=8 knees, Collins grade 1/2, 64-82 yr) were co-cultured with 4-5mm diameter synovium explants harvested from synovial joint capsule of the same knees. All procedures were approved by the Rush University Medical Center Institutional Review Board and the Committee on the use of Humans as Experimental Subjects at MIT. PTOA-like mechanical trauma was simulated by subjecting the cartilage surface of the osteochondral plugs to a single injurious unconfined compression of 60% strain rate to a peak stress of 5MPa using an incubator-housed loading apparatus. The study design included the following groups: (1) Mechanical injury (INJ) - injured osteochondral plugs were cultured in presence of pro-inflammatory cytokines (including TNF-α, IL-6 and IL-8) that were released by synovial explants and quantified by multiplex-readout in situ, (2) Treatment group (INJ + DEX): 100nM Dex was added to the cocultures of injured osteochondral plugs and synovial tissues immediately after injury. A preliminary science validation test was performed to identify a suitable mechanism to adapt CBS cocultures to the custom experiment module and the MVP facility. Engineering validation testing was then carried out to build logistical protocols for the spaceflight including transport of cultures and simulation of tasks preceding launch operations. Results: The levels of pro-inflammatory cytokines such as IL-6, IL-8 and TNF-α were upregulated in CBS cocultures. The combination of mechanical injury and increased release of inflammatory cytokines from synovial tissues caused extensive cell death and biochemical changes in both bone and cartilage. In the INJ group, cartilage tissue showed widespread cell death [Fig1 a], and subchondral bone showed increased cell death as well, indicated by numerous empty lacunae in the matrix. Biochemical analysis showed aggravated release of matrix component (including GAGs) into the medium, associated with cartilage degradation [Fig 1c]. Addition of Dex significantly reduced the injury-induced cell death [Fig 1b] and GAG loss by week 2 [Fig 1c]. For spaceflight preparation, tissue cards [Fig 1d] were optimized for long-term holding and maintenance of CBS co-cultures, which were placed into custom culture chambers [Fig 1e]. Multiple tests using this instrumentation were used to guide the design and operation of automated MVP facility [Fig 1f]. Investigation of disease biology and acute injury management is currently being tested in preparation for eventual spaceflight experiments in microgravity aboard ISS-NL. Conclusions: By providing a platform to study cartilage, bone and synovium together, our CBS MPS can potentially enable a more physiologically relevant understanding of tissue interactions that may lead to PTOA pathogenesis. This system can also be used to test the efficacy of therapeutics. In Space, this MPS will be used to explore the role of therapeutic agents to ameliorate cartilage degradation in microgravity to support astronaut health during long space missions.

Osteochondral Graft Size Is Significantly Associated With Increased Force and Decreased Chondrocyte Viability

Background: Insertion force has been shown to significantly reduce chondrocyte viability during osteochondral allograft transplantation. How graft size influences the required insertion force and chondrocyte viability has yet to be determined. Hypothesis/Purpose: The purpose was to characterize how graft size influences insertion force requirements and chondrocyte viability during osteochondral transplantation. The hypothesis was that larger grafts would require greater force and reduce chondrocyte viability. Study Design: Controlled laboratory study. Methods: Four graft sizes—15 × 5 mm, 15 × 10 mm, 25 × 5 mm, and 25 × 10 mm (diameter × depth)—were harvested from 13 thawed fresh-frozen human cadaveric distal femurs. Average, maximum, and cumulative force and number of impacts were recorded for 44 grafts by a surgical mallet embedded with a calibrated force sensor. In a separate experiment, fresh osteochondral tissues were subjected to mechanical loading. To capture a range of clinically important forces, categories were selected to correspond to impaction force data. Chondrocyte viability was assessed with confocal laser microscopy and live/dead staining. Results: Total force for all grafts averaged 4576 N. Median number of impacts for all grafts was 20 (range, 7-116). The mean number of impacts for 5-mm-deep grafts was 14.2 (95% CI, 10.8-18.6), as compared with 26.3 (95% CI, 19.9-34.4) for 10-mm-deep grafts (P < .001). The mean cumulative force for 5-mm-deep grafts was 2128 N (95% CI, 1467-3087), as opposed to 4689 N (95% CI, 3232-6803) for 10-mm-deep grafts (P = .001). For every 1 mm in graft depth, an average of 13.1% (95% CI, 6.2%-20.3%) more impacts are required when controlling for diameter and density (P < .001). For every 1 mm in graft depth, the force required increases on average by 17.1% (95% CI, 7.7%-27.4%) when controlling for diameter and density (P = .001). There was a significant reduction in chondrocyte viability for the forces required for graft thickness values >10 mm. Only forces associated with graft thickness <10 mm had chondrocyte viabilities consistently >70%. Conclusion: Insertion force increases significantly with increasing graft depth. Controlling for diameter and bone density, a 1-mm increase in graft depth is associated with 13.1% more impacts and 17.1% more force. Chondrocyte viability was significantly reduced to <70% at average forces associated with grafts thicker than 10 mm. Clinical Relevance: Based on the current data, graft depth is an important consideration for surgeons when sizing osteochondral allograft transplant for chondral lesions of the knee.

Résistance à l’arrachement d’une fixation hybride (Tape Locking Screw™) dans la reconstruction du ligament croisé antérieur. Une étude biomécanique sur os humain et porcin

IntroductionA novel hybrid anterior cruciate ligament (ACL) reconstruction technique known as Tape Locking Screw™ (TLS) is gaining popularity. Utilizing a suspension-type construct in conjunction with an interference screw, this technique has demonstrated successful initial clinical results with the use of quadruple hamstring graft. However, there is currently limited data available on the biomechanical strength of this fixation. This study investigates the pullout strength of the constructing human distal femora as well as in a porcine model. The construct is tested in isolation, without the use of any graft. We hypothesized that the pullout strength of this construct would be similar to or better than current fixation systems available. Materials and methodsThe Tape Locking Screw hybrid fixation system was implanted into 22 fresh frozen human distal femora (50–89 years old) randomized to 10×20mm titanium or polyether ether ketone (PEEK) screws by a single sports fellowship trained orthopedic surgeon. Given that the graft is secured to polyethylene terephthalate tape within the construct, the construct was implanted without any graft in order to isolate the device for biomechanical testing. After implantation, a tensile force was applied directly to the loop of tape at a loading rate of 5mm/min using an electromechanical testing system. The failure load was calculated from the resultant load-displacement curve. Specimens were then visually examined for mode of failure. Similar biomechanical tests were performed on 16 porcine femora. ResultsIn the human model, the mean pullout strength was 523±269N with the PEEK screw and 578±245N with the titanium screw. In the porcine femur model, mean strength was 616±177 N with PEEK, 584±245N with titanium. There was no statistically significant difference in failure loads between these four groups. Tape slippage at the screw bone interface was the primary mode of failure in all the groups tested. DiscussionOur results demonstrate that the hybrid technique provides excellent pullout strength in comparison to other soft-tissue ACL fixation methods, with tape slippage being the mode of failure in all specimens tested. This data, in addition to the advantages of the TLS system, support its consideration in the armamentarium of constructs available for soft-tissue ACL reconstruction. Type of studyLaboratory controlled study level 2.

Trabecular mapping: Leveraging geometric morphometrics for analyses of trabecular structure.

Trabecular microstructure of limb bone epiphyses has been used to elucidate the relationship between skeletal form and behavior among mammals. Such studies have often relied on the analysis of a single volume of interest (VOI). Here we present a method for evaluating variation in bone microstructure across articular surfaces by leveraging sliding semilandmarks. Two samples were used to demonstrate the proposed methodology and test the hypothesis that microstructural variables are homogeneously distributed: tali from two ape genera (Pan and Pongo, n = 9) and modern human distal femora (n = 10). Sliding semilandmarks were distributed across articular surfaces and used to locate the position of multiple VOIs immediately deep to the cortical shell. Trabecular bone properties were quantified using the BoneJ plugin for ImageJ. Nonparametric MANOVA tests were used to make group comparisons and differences were explored using principal components analysis and visualized using color maps. Tests reveal that trabecular parameters are not distributed homogeneously and identify differences between chimpanzee and orangutan tali with regards to trabecular spacing and degree of anisotropy, with chimpanzee tali being more anisotropic and having more uniformly spaced trabeculae. Human males and females differed in the pattern of trabecular spacing with males having more uniform trabecular spacing across the joint surface. The proposed procedure quantifies variation in trabecular bone parameters across joint surfaces and allows for meaningful statistical comparisons between groups of interest. Consequently it holds promise to help elucidate links between trabecular bone structure and animal behavior.

Pullout strength of a novel hybrid fixation technique (Tape Locking Screw™) in soft-tissue ACL reconstruction: A biomechanical study in human and porcine bone

IntroductionA novel hybrid anterior cruciate ligament (ACL) reconstruction technique known as Tape Locking Screw™ (TLS) is gaining popularity. Utilizing a suspension-type construct in conjunction with an interference screw, this technique has demonstrated successful initial clinical results with the use of quadruple hamstring graft. However, there is currently limited data available on the biomechanical strength of this fixation. This study investigates the pullout strength of the construct in human distal femora as well as in a porcine model. The construct is tested in isolation, without the use of any graft. We hypothesized that the pullout strength of this construct would be similar to or better than current fixation systems available. Materials and methodsThe Tape Locking Screw hybrid fixation system was implanted into twenty-two fresh frozen human distal femora (50–89 years old) randomized to 10×20mm titanium or polyether ether ketone (PEEK) screws by a single sports fellowship trained orthopedic surgeon. Given that the graft is secured to polyethylene terephthalate tape within the construct, the construct was implanted without any graft in order to isolate the device for biomechanical testing. After implantation, a tensile force was applied directly to the loop of tape at a loading rate of 5mm/min using an electromechanical testing system. The failure load was calculated from the resultant load–displacement curve. Specimens were then visually examined for mode of failure. Similar biomechanical tests were performed on sixteen porcine femora. ResultsIn the human model, the mean pullout strength was 523±269N with the PEEK screw and 578±245N with the titanium screw. In the porcine femur model, mean strength was 616±177N with PEEK, 584±245N with titanium. There was no statistically significant difference in failure loads between these four groups. Tape slippage at the screw bone interface was the primary mode of failure in all the groups tested. DiscussionOur results demonstrate that the hybrid technique provides excellent pullout strength in comparison to other soft-tissue ACL fixation methods, with tape slippage being the mode of failure in all specimens tested. This data, in addition to the advantages of the TLS system, support its consideration in the armamentarium of constructs available for soft-tissue ACL reconstruction. Level of evidenceLaboratory controlled study level 2.

Trabecular mapping of the human distal femur: Leveraging geometric morphometrics for studies of bone microstructure

Trabecular microstructure of limb bone epiphyses have been used to elucidate the relationship between skeletal form and locomotor behaviors among mammals. Such studies have often relied on the analysis of a single volume of interest (VOI) placed within the trabecular structure. Trabecular structure likely varies across continuous regions of bone and a single VOI will miss this variation, and much of the functional signal will be lost.Here I present a method for evaluating variation in bone microstructure across articular surfaces by leveraging sliding landmarks to sample multiple VOIs. 1007 sliding semi‐landmarks were distributed across the articular surface of 10 human distal femora using standard geometric morphometric procedures. Landmarks were then used to locate the positions of 1007 VOIs in the trabecular structure immediately deep to the cortical shell. VOIs were extracted and trabecular properties were measured for each VOI using BoneJ. Two questions are addressed: 1) are microstructural variables homogeneous across the articular surface? and 2) if microstructure is not homogeneous, are values of microstructural variables patterned on the condyles in a way that reflects human walking?Results suggest that trabecular microstructural variables are not homogenous across human femoral condyles. Bone volume fraction and trabecular thickness were greatest on the most inferior portions of the condyles, suggesting these areas reflect loading of the joint during normal walking. The technique presented here may have applications for reconstructing locomotion behavior of extinct animals as well as evaluating bone strength in clinical practice.

Ultrashort echo time magnetization transfer (UTE-MT) imaging of cortical bone.

Magnetization transfer (MT) imaging is one way to indirectly assess pools of protons with fast transverse relaxation. However, conventional MT imaging sequences are not applicable to short T2 tissues such as cortical bone. Ultrashort echo time (UTE) sequences with TE values as low as 8 µs can detect signals from different water components in cortical bone. In this study we aim to evaluate two-dimensional UTE-MT imaging of cortical bone and its application in assessing cortical bone porosity as measured by micro-computed tomography (μCT) and biomechanical properties. In total, 38 human cadaveric distal femur and proximal tibia bones were sectioned to produce 122 rectangular pieces of cortical bone for quantitative UTE-MT MR imaging, μCT, and biomechanical testing. Off-resonance saturation ratios (OSRs) with a series of MT pulse frequency offsets (Δf) were calculated and compared with porosity assessed with μCT, as well as elastic (modulus, yield stress, and strain) and failure (ultimate stress, failure strain, and energy) properties, using Pearson correlation and linear regression. A moderately strong negative correlation was observed between OSR and μCT porosity (R(2) = 0.46-0.51), while a moderate positive correlation was observed between OSR and yield stress (R(2) = 0.25-0.30) and failure stress (R(2) = 0.31-0.35), and a weak positive correlation (R(2) = 0.09-0.12) between OSR and Young's modulus at all off-resonance saturation frequencies. OSR determined with the UTE-MT sequence provides quantitative information on cortical bone and is sensitive to μCT porosity and biomechanical function.

Non-destructive electromechanical assessment (Arthro-BST) of human articular cartilage correlates with histological scores and biomechanical properties

The hand-held Arthro-BST™ device is used to map electromechanical properties of articular cartilage. The purpose of the study was to evaluate correlation of electromechanical properties with histological, biochemical and biomechanical properties of cartilage. Electromechanical properties (quantitative parameter (QP)) of eight human distal femurs were mapped manually exvivo using the Arthro-BST (1 measure/site, 5s/measure, 3209 sites). Osteochondral cores were then harvested from different areas on the femurs and assessed with the Mankin histological score. Prior to histoprocessing, cores were tested in unconfined compression. A subset of the cores was analyzed with polarized light microscopy (PLM) to assess collagen structure. Biochemical assays were done on additional cores to obtain water content and glycosaminoglycan (GAG) content. The QP corresponding to each core was calculated by averaging all QPs collected within 6mm of the core center. The electromechanical QP correlated strongly with both the Mankin score and the PLM score (r=0.73, P<0.0001 and r=-0.70, P<0.0001 respectively) thus accurately reflecting tissue quality and collagen architecture. Electromechanical QP also correlated strongly with biomechanical properties including fibril modulus (r=-0.76, P<0.0001), matrix modulus (r=-0.69, P<0.0001), and log of permeability (r=0.72, P<0.0001). The QP correlated weakly with GAG per wet weight and with water content (r=-0.50, P<0.0003 and r=0.39, P<0.006 respectively). Non-destructive electromechanical QP measurements correlate strongly with histological scores and biomechanical parameters providing a rapid and reliable assessment of articular cartilage quality.

Comparison of immature porcine and human bone mineral density about the knee

Background: Orthopaedic hardware pull-out studies frequently utilize various animal models to assess axial and multiplanar loading of bone. Biomechanical models and techniques for testing are common; however, bone quality measures frequently are not provided in published studies. Bone mineral density (BMD) and bone mineral content (BMC) are used for assessment of bone quality. The authors sought to determine whether immature porcine knees would be an appropriate model for human graft and hardware pull-out studies. Our hypothesis was that immature cadaver porcine knees (ICPK) would be less dense than those of healthy adult human distal femurs and proximal tibias and thus an inadequate model for human graft and hardware pull-out studies. Methods: This was an in vivo and in vitro comparative laboratory study of BMD and BMC between two human knee groups and ICPK. Eleven ICPK 3 mo in age (body mass 25.0±3.3 kg) were used. Human Group 1 consisted of 18 collegiate athletes with a mean age of 19.2±0.86 yr (body mass 76.1±14.4 kg). Human group 2 included 10 people with a mean age of 34.4±9.3 yr (body mass 79.3±5.9 kg). BMD and BMC were measured using a Lunar 10655/Prodigy DEXA Scanner and software. ANOVA tested differences among the three groups, and post hoc testing assessed differences between the groups. Results: Differences in BMD were shown among the three groups for distal femur (ICPK-0.91±0.11 g/cm2; HG1-1.17±0.34 g/cm2; HG2-1.2±0.32 g/cm2 [P=0.037]), and proximal tibia (ICPK-0.94±0.12 g/cm2; HG1-1.41±0.22 g/cm2; HG2- 1.26±0.17 g/cm2 [P=0.001]). Statistical differences were found among the three groups for femoral BMC (ICPK-3.51±1.25 g; HG1-7.5±3.06 g; HG 2-11.59±5.40 g [P=0.001]) and tibial BMC (ICPK-4.58±2.00 g; HG1-9.64±3.92 g; HG2-13.07±5.37 g [P=0.001]). Conclusions: BMD and BMC in the distal femur and proximal tibia of an immature pig are significantly less than that of an adult human. Testing of graft pull-out using an immature porcine model involving the bones about the knee may not be accurately extrapolated to humans. We believe our work illuminates the need for bone quality assessment and documentation with BMD and BMC when performing or comparing pull-out studies.

Anthropometric measurements of the human distal femur: a study of the adult Malay population.

The distal femurs of 100 subjects (50 men, 50 women) from the Malay population aged between 19 and 38 years were scanned to measure the anterior-posterior (AP) and medial-lateral (ML) width. The mean AP values were 64.02 ± 3.38 mm and 57.33 ± 3.26 mm for men and women, respectively, and the mean ML values were 74.91 ± 3.52 mm and 64.53 ± 3.07 mm. We compared our data to that published previously for the Chinese and Indian populations. It was found that the Malay population had smaller distal femur than that of the Chinese but was larger than that of the Indian population (P < 0.05). In conclusion, although it is well established that Asians have a smaller distal femur size than that of the Western population, the variations in different Asian ethnicities may need to be considered when designing the appropriate knee implant.

Quantitative ultrashort echo time (UTE) MRI of human cortical bone: Correlation with porosity and biomechanical properties

In this study we describe the use of ultrashort echo time (UTE) magnetic resonance imaging (MRI) to evaluate short and long T2* components as well as the water content of cortical bone. Fourteen human cadaveric distal femur and proximal tibia were sectioned to produce 44 rectangular slabs of cortical bone for quantitative UTE MR imaging, microcomputed tomography (µCT), and biomechanical testing. A two-dimensional (2D) UTE pulse sequence with a minimal nominal TE of 8 µseconds was used together with bicomponent analysis to quantify the bound and free water in cortical bone using a clinical 3T scanner. Total water concentration was measured using a 3D UTE sequence together with a reference water phantom. UTE MR measures of water content (total, free, and bound), T2* (short and long), and short and long T2* fractions were compared with porosity assessed with µCT, as well as elastic (modulus, yield stress, and strain) and failure (ultimate stress, failure strain, and energy) properties, using Pearson correlation. Porosity significantly correlated positively with total (R(2) = 0.23; p < 0.01) and free (R(2) = 0.31; p < 0.001) water content as well as long T2* fraction (R(2) = 0.25; p < 0.001), and negatively with short T2* fraction and short T2* (R(2) = 0.24; p < 0.01). Failure strain significantly correlated positively with short T2* (R(2) = 0.29; p < 0.001), ultimate stress significantly correlated negatively with total (R(2) = 0.25; p < 0.001) and bound (R(2) = 0.22; p < 0.01) water content, and failure energy significantly correlated positively with both short (R(2) = 0 30; p < 0.001) and long (R(2) = 0.17; p < 0.01) T2* values. These results suggest that UTE MR measures are sensitive to the structure and failure properties of human cortical bone, and may provide a novel way of evaluating cortical bone quality.

Study on the Microstructure of Human Articular Cartilage/Bone Interface

For improving the theory of gradient microstructure of cartilage/bone interface, human distal femurs were studied. Scanning Electron Microscope (SEM), histological sections and MicroCT were used to observe, measure and model the microstructure of cartilage/bone interface. The results showed that the cartilage/bone interface is in a hierarchical structure which is composed of four different tissue layers. The interlocking of hyaline cartilage and calcified cartilage and that of calcified cartilage and subchondral bone are in the manner of “protrusion-pore” with average diameter of 17.0 μm and 34.1 μm respectively. In addition, the cancellous bone under the cartilage is also formed by four layer hierarchical structure, and the adjacent layers are connected by bone trabecula in the shape of H, I and Y, forming a complex interwoven network structure. Finally, the simplified structure model of the cartilage/bone interface was proposed according to the natural articular cartilage/bone interface. The simplified model is a 4-layer gradient biomimetic structure, which corresponds to four different tissues of natural cartilage/bone interface. The results of this work would be beneficial to the design of bionic scaffold for the tissue engineering of articular cartilage/bone.

The Effective Mechanical Advantage of A.L. 129‐1a for Knee Extension

The functional significance of shape differences between modern human and australopithecine distal femora remains unclear. Here, we examine the morphological component of the effective mechanical advantage (EMA) of the quadriceps muscle group in a sample of hominins that includes the fossil A.L. 129-1a (Australopithecus afarensis) and modern humans. Quadriceps muscle moment arms were calculated from three-dimensional computer models of specimens through a range of knee flexion. All hominins were compared using the same limb positions to allow us to examine, in isolation, the morphological component of the lengths of the pertinent moment arms. After taking into account the differences in bicondylar angle, the morphological component of the EMA was calculated as the ratio of the quadriceps muscle and ground reaction force moment arms. Our analyses reveal that A.L. 129-1a would have possessed a morphological component of the quadriceps muscle EMA expected for a hominin of its body mass.